GitHub #183: Fix autonumbering of inlets/outlets

This addresses both the bug identified in the ticket with [outlet], and also
specializes the clone method to allow new inlets/outlets to take new numbers.
GitHub #180: Last bits on variable interpolation

Added monomix.mfp, which demonstrates the [loadbang]-based variable interpolation
scheme.  Mentioned it in the README.  Ensures that [loadbang] is called on
cloning a scope.  Add a LexicalScope.clonenum to give patches access to which
copy a particular layer is working in.